Bureau of Mineral Resources, Geology & Geophysics
RECORD 1990/59
REPORT ON THE GEOLOGY OF THE LEONORA AREA, WESTERN
AUSTRALIA
Cees W. Passchier iJi' __
A publication from the National Geoscience Mapping Accord -Eastern Goldfields Project
; )
RECORD 1990/59
REPORT ON THE GEOLOGY OF THE LEONORA AREA, WESTERN
AUSTRALIA
Utrecht, december 1989
Cees W. Pas schier IV A - Utrecht University - Budapestlaan 4 - The Netherlands
A publication from the National Geoscience Mapping Accord -Eastern Goldfields Project
~Commonwealth of Australia, 1990 This work is copyright. Apart from any fair dealing for the purposes of study, research, criticism or review, as permitted under the Copyright Act, no part may be reproduced by any process without written permission. Inquiries should be directed to the Principal Information Officer, Bureau of Mineral Resources, Geology and Geophysics, GPO Box 378, Canberra, ACT 2601.
•
REPORT ON THE GEOLOGY OF THE LEONORA AREA, WESTERN
AUSTRALIA
Utrecht, december 1989
Cees W. Pas schier
IVA - Utrecht University - Budapestlaan 4 - The Netherlands
Abstract
Deformation in the Archaean greenstone belt and granitoid rocks of the Leonora district comprises at least three phases of deformation. D 1 is a phase of displacement
along gently dipping ductile shear zones. A shape fabric developed in the zones, dominantly by N-directed movement of the hanging wall. D2 is a phase of NE-SW
shortening and minor NW-SE transcurrent dextral movement along steeply dipping ductile shear zones. D 2 caused development of upright folds in bedding and S l' D3
caused local folding and development of a weak foliation.
Introduction
The Leonora District is situated in the eastern part of the Archaean Yilgarn Craton of
Western Australia. The area is characterised by deformed and undeformed granitoid
plutons, separated by linear greenschist to amphibolite facies greenstone belts. In the
Leonora district, shear zones are common in all lithologic units, and are specifically
well-developed along the contact of the granitoid plutons and the greenstone belts.
The area around Leonora has been described by Hallberg (1983, 1985), Thorn and
Barnes (1977), Skwarnecki (1987) and Williams et al (1989). Williams et al (1989)
have shown that a complex pattern of shear zones exists in the Leonora area, and that
gold mineralisation may be linked to some of these shear zones.
During june-july 1989 an analysis was made of a number of the shear zone
structures near Leonora, with the aim to provide a more detailed account of their
2
structural history. This repon presents fIrst results of this research project, based on
the field data. Work was mainly concentrated in two areas: (1) a narrow strip of
deformed quartzite, slate and felsic volcanics between Leonora and Mount Newman,
described here as the Mount George zone (Fig. 1) (Mount George shear zone
according to Williams et al. 1989); and (2) a shear zone which follows the contact of
the Rhaeside granite west of Leonora and the greenstone belt (Fig. 1). Work along
this shear zone was meanly concentrated around the Jasper Hills (Fig. 1 & 2).
Geological Setting
The area around Leonora consists of poorly exposed plutons of granodiorite,
adammellite and granite, alternating with greenstone belts (Fig. 1). The greenstone
belts consist mainly of mafic and felsic metavolcanics, and minor amphibolite,
metagabbro, quartzite, banded iron formation (BIF), ultramafics and intrusions of
porphyry and dolerite. Rhythmically laminated beds of quartzite, up to 100m thick,
occur in the Mount George zone, and adjacent to the Rhaeside granite west of
Leonora (Fig. 1,2). West of the Mount George zone, mafic and ultramafic rocks
with occasional strips of slate and thin lenses and layers of ferruginous and siliceous
BIF dominate. The quartzite beds in the Mount George zone are bounded on the
western side by a strip of slate up to 500m wide. East of the Mount George zone,
felsic metavolcanics dominate with minor mafic metavolcanics and quartzite lenses.
Structural analysis was concentrated around the quartzite beds because they
crop out well, and allow a single stratigraphic horizon to be followed over a large
distance, outlining the large scale structure. In the case of the Mount George zone, a
single quartzite horizon could be followed over 65 km.
Deformation sequence
D 1 structures
A weak mica foliation or planar shape fabric (Sl) and associated stretching lineation
or mineral lineation (Ll) form the earliest structures in the area. Sl and Ll do not
occur as penetrative fabric elements throughout the Leonora area; they have sofar only
been recognised around Mount Newman, along the contact of the Rhaeside granite
3
(Fig. 1, 2), and near Mount Malcolm 10 km E of Leonora. In granite and mafic
volcanic along the contact of the Rhaeside granite, S 1 and Ll are only locally
developed in shear zones surrounding undeformed lenses. The patchy occurrence of D 1 structures over the area is therefore at least partly an original feature due to
localised deformation in shear zones. Later deformation erased or transposed Dl
structures elsewhere. The dramatic decrease in stratigraphic thickness from NW to SE
between the quartzite layers in the Mount George zone and along the Rhaeside granite must also be a Dl effect; the strain intensity of later phases of deformation cannot
account for this change in thickness (P. Williams, pers. comm.). In the Mount Newman area, Sl is present in slates without an associated
stretching lineation (Fig. 2). Sl is gently N-dipping here, while So dips more steeply
to the north (Fig. 1). In the Jasper Hills area, Sl and Ll are well developed in all
lithologic units. Sl is best developed at the contact of granite and mafic volcanics
(Fig. 3), and in BIF layers. In BIF layers, the Ll stretching lineation is parallel to
isoclinal fold axes. In quartzite, Dl deformation gave rise to spectacular ellipse
shaped aggregates on bedding surfaces, defining a linear and planar shape fabric. Ll
is moderately NNE plunging in the Jasper Hills area (Fig. 4 - cf. Williams et aI,
1989). An interesting feature of the Jasper Hills area is the oblique orientation of Sl
in mafic volcanics and in BIF on two sides of a NW -SE trending D2 shear zone (Fig.
3); in the west, Sl is subvertical NS trending; in the E, it is gently N-dipping. This
feature is probably an original major Dl structure, since Ll orientation is identical on
both sides, and the pole to the greatcircle best-fit of Sl poles coincides with the center
of the Ll orientation cluster (Fig. 4b-4c); it can be interpreted as a mega-scale FI
sheath fold in the contact zone of mafic volcanics and granite, now transected by D2
and younger shear zones. Outside the Jasper Hills area, an Sl foliation is subparallel to the contact of the
Rhaeside granite with the greenstone belt, from the Diorite King mine in the W, to
the Sons of Gwalia mine S of Leonora (Fig. 1, 2). Stretching lineations have a
variable orientation along this shear zone, as discussed in Williams et al. (1989), and
below.
4
D 2 structures
D 2 is the most prominent phase of defonnation in the area. It caused development of
open to tight upright folds with subvertical to steeply NE dipping axial planes and a penetrative steeply NE or SW dipping slaty cleavage (S2) in some areas (Fig. 4d,e;
Williams et al, 1989). In the Mount Newman and Jasper Hills areas, open F2 folds
develop in Sl' In the Jasper Hills area and in the Victoria Wells mine, dextral D2
shear zones transect S l'
A major NNW-SSE trending shear zone, several kilometres wide (the Keith
Kilkenny tectonic zone of Hallberg 1985) is located to the east of Leonora (Fig. 1, 2). This zone is interpreted as a D2 structure, since the orientation of the foliation in
the zone can be traced into S2 in adjacent areas where it overprints E-W trending SI'
In the Keith-Kilkenny tectonic zone, S2 is strong and NW -SE trending (Fig. 4d). An
L2 stretching lineation is present in felsic volcanics in zones of high strain up to 100
m wide. L2 is gently NW or SE plunging (Fig. 4h). The Keith-Kilkenny tectonic
zone is interpreted as the domain in which D2 structures are most strongly developed,
and early fabric elements are transposed.
D3 structures
Effects of D3 defonnation have been observed only near Mount George, and in the
Mount Newman area (Fig. 2). Between Mount George and Station Creek, a large
fold (the Station Creek Fold; Fig. 2) is developed in the Mount George zone. It defonns S2 which locally trends subparallel to So in the quartzite. Axes ofF3 folds,
parasitic on the main Station Creek Fold, have a strongly variable orientation
depending on the orientation of the fabric element in which they developed (Fig. 4j). Intersection lineations of S2 and S3 plunge gently to the NNW or SSE (Fig. 4j). S3 is
locally developed as a crenulation cleavage, especially in the zone up to 5 km N of the Station Creek Fold, and trends NNW-SSE (Fig. 4k). S3 fans strongly in this area;
where the S2 enveloping surface is steep, S3 is gently dipping; where S2 has a
shallow dip, S3 is steep.
5
Around Mount Newman, a subhorizontal S3 is locally overprinting a steep S2'
As the dip of Sl is commonly also gentle, the local structure is difficult to interpret in
many outcrops. The presence of three foliations has, however, been confinned in
some outcrops (Fig. 5).
Discussion
Sense of shear during Dl
D 1 shear zones usually lack suitable sense of shear markers in the field; bedding is
commonly subparallel to Sl and must have been near the developing foliation to start
with. Where sense of shear can be detected from deflected bedding or foliation planes
however, as in some shear zones in the Rhaeside Granite at Jasper Hills and Diorite
King mine, and in the Victoria Wells Mine (Fig. 6, 7), movement is normal (upper
block to the N). This confirms observations in the Harbour Lights and Sons of Gwalia Mines, where the dominant (D
1) deformation resulted in normal shear zone
movement, i.e. uplift of the granite relative to the greenstone belt which lies to the E
and NE (Skwarnecki, 1987; Williams et aI, 1989). The asymmetry of fibre packets
around spherical pyrite aggregates in an outcrop of slate with a gently N-plunging
stretching lineation on the Leonora - Malcolm railway, 10 km east of Leonora, also
indicates normal movement (Fig.8). This illustrates that early normal movement is not
only restricted to the granite-greenstone contact. One should bear in mind, however, that the normal movement on Dl shear zones only reflects present orientation of the
zones, and original orientation may have been different; the Dl shear zones may even
have originated as thrusts with N-directed movement.
orientation of Dl structures
Sl in the Leonora area has been recognised where it is overprinted by D2 fabric
elements. Since D2 structures trend dominantly N-S, Sl is mainly found in an oblique
(E-W) orientation. This does not mean, however, that Sl was everywhere E-W
trending before the onset of D2 For example, crenulated Dl fabric elements are
absent in most of the Keith-Kilkenny tectonic zone, although a refolded Sl is present
6
to the east and west. This may mean that D1 structures were destroyed by strong D2
deformation, but alternatively D1 structures may have been N-S trending in this area
before the onset ofD2.
sense of shear in the Keith-Kilkenny tectonic zone
In the Keith-Kilkenny tectonic zone several fabric elements indicate that sense of
shear is dextral, rather than sinistral as suggested by Williams et al. (1989). This is
based on the persistent a-type asymmetry of feldspar porphyroclasts in felsic
volcanics (Pas schier & Simpson, 1986), asymmetric boudins and shear band foliation. A dextral shear sense could also be determined in a 30 cm wide D2 shear
zone in mafic metavolcanic rocks in the Victoria Wells mine (Fig. 6). This sense of shear was based on deflection of a D1 shear zone (Fig. 6), and a shear band cleavage
in the D2 zone. The western limit of the Jasper Hills area is affected by a dextral D2
shear zone, which has been reactivated by a late transcurrent fault (Fig.3; enlarged domain); S1 and L1 stretching lineations have here been deflected by the D2 shear
zone.
significance of the Mount George zone
A strip of lenses of quartzite, slate, quartz-sericite phyllonite and chlorite schist, here
described as the Mount George zone, can be followed over 65 km from Mount
Newman down to south of Leonora (Fig. 1,2). Williams et al. (1989) use the term
Mount George shear zone for this strip and regard it as a late sinistral transcurrent
ductile shear zone which postdates a regional phase of shortening and upright folding
(D2)' Their main arguments are:
(1) brittle faults with sinistral shear sense occur in the Mount George Zone SE of
Mount Newman (Fig. 1);
(2) gently trending stretching lineations occur in quartzite, slate and quartz-sericite
phyllonite in the Mount George zone south of Mount Davis (Fig. 1).
Other fabric elements which seem to indicate sinistral shear sense along the
zone are (Williams et al. 1989);
(3) quartz fabric data from the Mount George zone near Leonora;
7
(4) the flexing of bedding in mafic and felsic volcanic rocks east of Mount George
(Fig. 1, 2).
(5) the shape of the Station Creek Fold, which is interpreted as a drag fold in the
shear zone.
Detailed work along the entire length of the Mount George zone has shown,
however, that the zone cannot be regarded as a shear zone in the sense of a 'zone of
high strain, developed by non-coaxial progressive deformation'. The strain intensity
in and around the quartzite is in many places not stronger than in mafic volcanics to
the west and east. No asymmetric structures which could be associated with non
coaxial flow have been observed along the Mount George zone north of Station
Creek. I therefore prefer the term Mount George zone over the term 'Mount George
shear zone' used by Williams et al. (1989). The Mount George zone is interpreted as the eastern limb of a 100 km scale F2 antiform (Figs. 1,2). S2' which overprints Sl
in symmetric F 2 folds around Mount Newman, can be followed along the Mount
George zone with a consistent vergence of S2-S0 down to the Jasper Hills area (Fig.
2). S2-S0 intersection lineations (Fig. 4g) and F2 fold axes plunge dominantly to the
NNW. From Station Creek to the south, the structural setting of the Mount George zone changes; S2 is subparallel to So in this area (Fig. 2), and an L2 stretching
lineation appear on S2 surfaces. Sheath folds can be found in bedding in the quartzite
in this area. An L2 stretching lineation is also visible in adjacent slates and felsic
volcanics, associated with S2' The rhythmic sedimentary layering in the quartzite,
very clear at Mount Newman and still recognisable farther S, is erased by high strain
in the section south of Station Creek; also, the quartzite thickness is generally less
than in the N. All these features can be attributed to increasing strain from Station creek to the south as an effect of the influence of the major dextral D2 shear zone
which lies to the east of Leonora (Keith-Kilkenny tectonic zone).
The arguments used by Williams et al. (1989) for the Mount George zone to
be a sinistral shear zone can be accounted for as follows; (1) the sinistral brittle faults near Mount Newman belong to a late (post-D2 ) phase of
faulting which is unrelated to the foliation present in the Mount George zone further
south; they have not been found elsewhere along the Mount George zone. It is not clear whether these faults are related to D3 as described above;
(2) the stretching lineation in the Mount George zone near Leonora is an effect ofD2
deformation in the Keith-Kilkenny tectonic zone;
8
(3) quartz fabrics (Williams et aI, 1989) are largely symmetrical and their weak
asymmetry may only indicate local flow partitioning or local (small) deviations from
bulk near-coaxial flow. In several outcrops of the quartzite along the Mount George
zone, quartz veins were found which have been strongly but coaxially flattened and
folded; this also gives evidence for near-coaxial deformation in the quartzite during D 2' possibly as an effect of flow partitioning. Further research will be carried out on
quartz samples from these outcrops.
(4) the flexing of bedding in mafic and felsic volcanic rocks east of Mount George is an attenuated F 2 fold limb (Fig. 2).
(5) the Station Creek fold, which seems to indicate sinistral shear sense on the map, is younger than S2 and apparently the result of hulk coaxial shortening. Also, an
apparent F2 fold in dolerite in the Keith-Kilkenny tectonic zone which would be
consistent with a sinistral shear sense, intruded along folded bedding during D2 (Fig.
9); it transect S2' and is largely undeformed in the 'fold closure'. The dolerite
apparently intruded parallel to (folded) bedding. A minor dextral D2 shear zone
transects the curved dolerite on its eastern limb (Fig. 9). No interference of this shear
zone with foliation in the wall rock is evident, suggesting that the shear zone
developed as part of the same phase which formed the transected foliation.
Flow during D2 in the Keith-Kilkenny zone
An apparent contradiction to the role of the Keith-Kilkenny zone as a dextral shear zone is the fact, that bedding in both limbs of the large F 2 fold east of Mount George
(Fig.l, lOa) is stretched, not shortened. This would be easy to explain if these limbs were deformed in pure shear normal to S2 (Fig. 1Ob,c), but this does not agree with
the numerous asymmetric features found which indicate that D2 developed by non
coaxial dextral transcurrent flow. Dextral simple shear at a small angle to S2'
however, would lead to shortening of the western limb of the F2 antiform in Figure
10. Most likely, deformation was by general non-coaxial flow with both pure shear
and simple shear components (Fig. 1Ob, c; centre). Local partitioning of flow into
nearly coaxial parts and nearly simple shear parts can explain why some domains
show development of 'simple shear' ductile shear zones (e.g. the one transecting the undeformed dolerite NE of Leonora), while elsewhere S2 seems to have formed in
9
coaxial deformation (most of the Mount George zone between Station Creek and
Mount Newman).
The shear zone along the Rhaeside granite contact
Jasper Hills area
Some problems are associated with interpretation of the shear sense in the D 1 shear
zone along the contact of the Rhaeside granite at Jasper Hills (Fig. 2). The western domain of the Jasper Hills quartzite near the D2 shear zone (Fig. 3 inset), shows a
very strong linear and planar shape fabric in the quartzite. Williams et al. (1989)
measured quartz fabrics in these quartzites (from this site and up to 1 km to the E),
which clearly indicate S-directed thrusting of the upper block. They interpreted this deformation as Dr This creates a regional problem, however, since sense of shear
for Dl elsewhere in the contact shear zone is a N-directed movement of the hanging
wall (Le. relative uplift of the granite). While more measurements of quartz fabrics will have to be made to solve this problem, it is possible that the strong D2
deformation in the western side of the Jasper Hills quartzite caused deflection of the
quartzite from an E-W to a NW -SE trend, and a local strong shape fabric; farther east
along the zone, quartzite fabrics are much weaker. In the NW of the Jasper Hills area
(Fig. 3, inset), a deflection of the quartzite and local strain increase has been observed
near a dextral shear zone; since orientation of lineations in this zone and elsewhere in
the quartzite do not coincide, the structure must have formed by two consecutive
phases of deformation. As such, it is possible that the thrust-sense measured in crystallographic preferred orientation fabrics in the quartzite is due to D2 overprint;
since S2 and D2 shear zones are dominantly E dipping in this area, sense of shear on
the D 2 mobile zones was locally dextral thrusting
eastern granite contact
The strongly mineralised domain in the shear zone along the eastern edge of the
Rhaeside granite near Leonora shows a complex deformation sequence in which an
10
early foliation (Sl) and stretching lineation (L1) can be distinguished with steep
easterly dip and plunge respectively. Since SI trends everywhere parallel to the
granite-greenstone contact in the west, and D2 features increase in importance to the
east, the zone along the eastern edge of the granite may be a zone of 01 and 02
interference. In Victoria Wells mine, both 01 and 02 shear zones are present. In
Trump mine (Fig. 1), sense of shear in some pits indicates SSW-directed subhorizontal thrusting. probably an effect of D2 as well. Nevertheless, no obvious
overprint of Dl features by D2 occurs in the mines farther south. This can be
explained if the original orientation ofDl structures was such, that they were lying in
the instantaneous extension field ofD2 flow, i.e. NW to NNW trending (Fig. 7c); in
that case, D2 would result only in reorientation and further stretching and flattening of
existing structures. The steep eastern side of the granite may be be an effect of the major D2 Keith-Kilkenny tectonic zone, overprinting an originally gently dipping
granite-greenstone contact.
possible influence of later deformation
Finally, deformation postdating D2 may have affected the contact shear zone near
Leonora. Williams et al (1989) have shown, that the plunge direction along the
contact shear zone of the Rhaeside granite changes from NE plunging in the north
(Jasper Hills, Victoria Wells) through E-plunging (Harbour lights) to SE plunging
(Sons of Gwalia) in the south. This may be either an original feature (it could be
tentatively associated with gneiss doming), or an effect of reorientation in later deformation. It is significant that the plunge of the L2 stretching lineation in the
Mount George zone changes equally near Harbour lights; in Leonora, L2 is gently
south plunging, N of Harbour lights L2 passes through subhorizontal to a northerly
plunge; near the Station creek fold, plunges are 20-350 ; further north the plunge of
the lineation increases further, although the lineation itself becomes weaker and disappears around Mount Davis. The change in direction ofDI and D2 structures near
the same site could be coincidental, but the presence of a gentle open fold of post-D2 age with E-W trending fold axis cannot be excluded
1 1
Mineralisation
Williams et al. (1989) have shown, that mineralisation around Leonora is virtually restricted to D 1 shear zones. This does not explain the erratic pattern of mineralisation
along the Dl shear zones, however. In the Victoria Wells mine, mineralisation seems
to occur notably at the intersection of solitary Dl and D2 shear zones. It will be
interesting to see whether it is in fact at the interference of Dl and D2 shear zones
where mineralisation is common; it is remarkable that the most productive mines are situated in a zone of proposed strong Dl and D2 interference north of Leonora.
Clearly, this possibility warrants further research.
Conclusions
(1) At least three phases of deformation are present in the Leonora area; (2) Dl was dominantly a phase of displacement along gently dipping shear zones with
movement of the hanging wall towards the north; this is especially obvious in the Jasper Hills and Mount Newman areas. Dl deformation is mainly concentrated in the
contact zone between greenstone belts and granite, and locally in the greenstone belts. Along the contact, both a slaty cleavage (S 1) and a stretching lineation (L1) are
usually present. (3) D2 structures are present throughout the area. D2 caused development of the
penetrative regional slaty cleavage S2' D2 was a phase of dextral transcurrent non-
coaxial deformation with NE-SW trending instantaneous shortening direction and
NW-SE tending extensional 'shear plane'. Flow vorticity seems to have varied strongly over the area. Presence of a major D2 shear zone around and east of
Leonora (the Keith-Kilkenny tectonic zone) caused local strong foliation and lineation
development, and probably steepening of the E-side of the granite.
(4) The sinistral Mount George 'shear zone' described by Williams et al (1989) does not exist as such: it is a large scale F 2 fold limb in a stratigraphic horizon dominated
by quartzite beds; its southern part lies in a D2 shear zone, but the movement sense on
this zone is dextral.
12
(5) The coincidence of quartzite lenses and layers with shear zones in the area is
probably a topographic effect, the result of shear zones transecting relatively flat lying
stratigraphy at depth.
Acknowledgements
I wish to thank Peter Williams for fruitful cooperation and many stimulating
discussions in the field, mostly on Sunday trips between long weeks of mapping. A
review by Alistar Stewart improved the manuscript. A grant from the Dutch Dr.
Schlirmann Fund is gratefully acknowledged.
References
BMR 1989. Gold potential of early shear zones near Leonora, WA. BMR Research
Newsletter 10, 6-7.
BMR 1990. Sons of Gwalia gold deposit, W A; localisation in an Archaean
extensional ductile shear zone. BMR Research Newsletter 12, 8-9.
Hallberg, J.A. 1985. Geology and mineral deposits of the Leonora-Laverton area,
northeast Yilgarn Block, Western Australia. Hesperian Press, Western Australia.
Pas schier, C.W. & Simpson, C. 1986. Porphyroclast systems as kinematic
indicators. J. Struct. Geol. 8; 831-843.
Skwarnecki, M.S. 1987. Controls on Archaean gold mineralisation in the Leonora
district, Western Australia. in Ho, S. E. & Groves, D.I. (eds) Recent advances in
Understanding Precambrian Gold deposits. Geology department and University
extension, University of Western Australia.
Thorn, R. & Barnes, R.G. 1977. Leonora, Western Australia. Geological Survey of
Western Australia 1:250000 Geological Series Explanatory Notes, Sheet SI/50-8, 24
pp.
13
Williams, P.R., Nisbet, B.W., and Etheridge, M.A. 1989; Shear zones, gold
mineralisation and structural history in the Leonora District, Eastern Goldfields
Province, W A. Australian Journal of Earth Sciences 36, 383-403.
14
......... : •• : •••••••• : ••••••••••• / •• "0:
Diorite King
~
[2]
B
t
granite
dolerite
quartzite
So Sl Ll S2 L2 02
mmor shear zone
: ............. ~ ........... ~J. .................... . lOkm
Rhaeside granite
Fig. 1 - Schematic map of the geology NW of Leonora, WA. Lithology details have been omitted from the greenstone belts (white) in order to show detail in structure of quartzite beds.
quartzite
general
1 ~ D2 shear sense
Jasper Hills
Victoria Wells
(Station Creek Fold)
1~ K~ith-'1'\ \ \ \ \\ KIlkenny 'i, \ \ \ 'T' • , \ \ \ \ \ 1 ectomc
\ \ \ \ \ \ \ \ \ \ \ \ Zone , \ \
\ \ \ \ \ \ \ \ \ \ \
\ \ \ \ \ \ \ n
\ \ \ \ \ \ \ \ \ \ \ \
\
Leonora \
Fig. 2 - Cartoon outlining the large scale structure of the Leonora area
, strain in quartzite
" 44
4~/J 501,//
• quartzite
mafic volcanics
II BIF in mafic volcanics
• ultramafic
f:::':::':::':~':::':J granite
felsic volcanics
porphyry
quartz vein
, ...... """ D2 shear zone
I kIn
Fig 3 - Map of the Jasper Hills area. Inset shows geology and strain intensity in a quartzite lens Ls - stretching lineation
• •
++ + +
+ •
+ ••
+ + + +* + + ~+ +
+ +e+ • •
a •
• •• • .1 + ~ ... ., .. .. :+.: . ,' .
a • a
•
a
+
a ••
+ • ++ •
• + +
• • •
+
Jasper Hills
BIF • + quartzite
• Mount George zone (outside Station Creek fold domain)
+ MtNewman a
Keith-Kilkenny tectonic zone
Station Creek fold
Fig. 4a - bedding
Equal Area
•• •
• • •
.... .
Fig. 4b - S 1 foliation
Equal Area
•
I -.I
•
•
• •
• •
• • • • • • • • • • • • • •• . , . ·1 .• " . : ....... • .... . ..... • • • ••• r •• • • : .(: . • •• • • :
• • •• • • • • • • • • • • • •
+ • • • •
• •
Fig. 4c - Ll stretching lineations
•
•
• •
Ll
•
• •
Equal Area
o o 0
+
o
o
o 0' 0
fo 0 ,,, 0
~o'ooo -. t o
°i 0 .. 1 o
Fig. 4d - S2 foliations
o
D
D
+
+ o
o
+
+
a a
+ a 0 a
o
+ +
++ D
+
+ Mt Newman area
a Station Creek fold
o o
Keith-Kilkenny tectonic zone
Equal Area
8 2
Jasper Hills
• •
• + • • • • •
•
Equal Area
• total •
• • •
• • • •• • .... . ~ ' . • • •• r • • • • •
+ • • • • •
• • • •
• •
Fig. 4 e - S2 foliations
Equal Area
Fig. 4f - F2 foldaxes
+ + +
+ +. + ...
++ +
+
• .+
•
+ •
Fig. 4 g - intersection lineations SO-S2
+
• • ••• • a :I- • a •• + .... a +.
+. +. a a + a.+
• a
+
+
Fig. 4h - L2 stretching lineations
•
+
+
•
F2 foldaxes
• F2 sheath fold axes (southern Mount George zone)
+ F2 axes open folds MtNewman
intersection lineations SO-S2
• Keith-Kilkenny tectonic zone
+ Northern Mount George zone
stretching lineations D2
• Keith-Kilkenny tectonic zone
+ Station Creek fold
a Southern Mount George zone
•
Equal Area Station Creek fold +
• F 3 fold axis
• + Intersection • lineation • +
• S2-S3
• •
+ • •
• + • + +
+ + + + +
Fig. 4 j - D3 linear structures
Equal Area
• Station Creek fold
• + Mount Newman • •
• + +
• + +
• + • • •
Fig. 4k - S3 foliation
•
East West lern
Fig. 5 - Sketch of interference of 01-02 and 03 structures in an outcrop near Mount Newman.
•
\ 0, shear zon~\
\\\ \\\\ \\\\\\ ',\\\\\\ \\\\\\\ \\\\\\\\ \\\\\\\\ 1..\\\\\\ \\\\\\ ,\\\\\ \\\\\ \\\\\ \\\\\ \ \ \ \ \\\ \\\ \\\ \\\ \\ \\ \\
\
0., shear zone
North
Victoria Wells Mine
10C) 111
Fig. 6 - Schematic map of the structure in Victoria Wells mine. Ornamentation indicates foliation in the metabasite wall rock.
•
Victoria Wells Mine
""'''''' "''''''' SI wall rock --- Dl shear zone - - - - - D shear zone 2
• Ll + L2
I ~ ,I I'
II I I
, I , I , ,
" , , ,
Dl : sinistral normal D2 : dextral thrust
Fig. 7 - Orientation data from the Victoria Wells Mine
•
1 em,
Fig. 8. Fibrous quartz fringes surrounding spherical pyrite aggregate in slate in a section normal to SI and parallel to an Ll stretching lineation. The geometry of the fringes indicates dextral shear sense. Slate outcrop on railway, 10 km east of Leonora.
I I I I I I I I I I
L~21 I 1 I~ I I 1
:t~~1 71 II I ~II I 1 I I I 1 I I
1 I I t
I I I I I 1 I
I ~2 I I I I
114 1111
I \1 I I I
: I~~~ I I I 16']1 I I I '-'I I
I I 1 I I I I I
I I I I 1 I 1 I I I I I I I I I I I I 1 I I I I I I 1 I 1 I I I
B felsic volcanics
dolerite
'" bedding
--It- 'of(.. planar shape fabric
J4 linear shape fabric .... _ .... .. shear zone
I I 1 I 1
1 ~tll h ~~:: 1 I 80 I I I I I 1 I 1 I 1 1 I I I I I I I I I I I I
1 I 1 I I 1 I 1 I I
I I I I I I I I 1 1 I I 1 I :t Bl I I 1 I
1 I I I I I I I I I I I
I I I I I I I I I I I I I I I I
I I I
I I
N
I I I I I I I I I I I I I I I I I I I I
250m I I I I I I I I I I I
I 1 I 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I
Fig. 9. Dolerite dyke which intruded along D2-folded bedding in felsic volcanics in the Keith -Kilkenny tectonic zone. The undeformed dolerite is transected by dextral D2-shear zones in which the shape fabric elements have the same orientation as in the felsic volcanics.
(a)
• Leonora
(b) simple shear
(c)
general pure shear
f' l' \~,~ w~l/
-rM" 1;;W:Z-
bedding --irrotationalline in flow
instantaneous stretching axis
Fig. 10 - explanation for the D2 defonnation pattern near Leonora, where both limbs of F2 folds undergo extension in non-coaxial dextral transcurrent deformation;(a) map of bedding and 82 orientation in major F2 folds; (b) different possible flow types for D2; (c) orientational relationship of the domain of shortening (striped) and bedding (grey) for the different flow types.The orientation of bedding and S2 (a) around Leonora is difficult to explain by simple shear (b), since some limbs of F2 folds would undergo shortening (c) during progressive defonnation, and rotate dextrally away from the flow plane. The situation could be explained by pure shear (b,c) where both fold limbs are in the extensional domain and rotate towards the principal extension axis. This does not agree with the occurrence of dextral sense of shear markers, however. The situation is best explained by general non-coaxial flow (between pure and simple shear) during D2 deformation: both fold limbs are in the extensional domain and rotate towards the principal irrotational axis; the foliation plane also rotates to this axis.
